title: Mutation screen of the SIM1 gene in pediatric patients with early-onset obesity.
abstract: BACKGROUND
  The transcription factor SIM1 (Single-minded 1) is involved in the control of food intake and in the pathogenesis of obesity. In mice, Sim1 is involved in the development of the paraventricular nucleus, and Sim1 deficiency leads to severe obesity and hyperphagia. In humans, chromosomal abnormalities in the SIM1 gene region have been reported in obese individuals. Furthermore, recent data also suggest that loss-of-function point mutations in SIM1 are responsible for SIM1 haplo-insufficiency that is involved in causing human obesity. In this study, we therefore wanted to expand the evidence regarding the involvement of SIM1 mutations in the pathogenesis of severe early-onset obesity.
  
  
  METHODS
  We screened 561 severely overweight and obese children and adolescents and 453 lean adults for mutations in the coding region of the SIM1 gene. Mutation screening in all patients and lean individuals was performed by high-resolution melting curve analysis combined with direct sequencing. To evaluate the effect of the mutations on SIM1 transcriptional activity, luciferase reporter assays were performed.
  
  
  RESULTS
  Mutation analysis identified four novel nonsynonymous coding variants in SIM1 in four unrelated obese individuals: p.L242V, p.T481K, p.A517V and p.D590E. Five synonymous variants, p.P57P, p.F93F, p.I183I, p.V208V and p.T653T, were also identified. Screening of the lean control population revealed the occurrence of four other rare SIM1 variants: p.G408R, p.R471P, p.S492P and p.S622F. For variants p.T481K and p.A517V, which were found in obese individuals, a decrease in SIM1 transcriptional activity was observed, whereas the transcriptional activity of all variants found in lean individuals resembled wild type.
  
  
  CONCLUSIONS
  In this study, we have demonstrated the presence of rare SIM1 variants in both an obese pediatric population and a population of lean adult controls. Further, we have shown that functional in vitro analysis of SIM1 variants may help in distinguishing benign variants of no pathogenic significance from variants which contribute to the obesity phenotype.
authors.affiliation: Department of Medical Genetics, University of Antwerp and Antwerp University Hospital, Antwerp, Belgium.
authors.forename: D
authors.initials: D
authors.lastname: Zegers
authors.affiliation: Department of Medical Genetics, University of Antwerp and Antwerp University Hospital, Antwerp, Belgium.
authors.forename: S
authors.initials: S
authors.lastname: Beckers
authors.affiliation: Department of Medical Genetics, University of Antwerp and Antwerp University Hospital, Antwerp, Belgium.
authors.forename: R
authors.initials: R
authors.lastname: Hendrickx
authors.affiliation: Department of Medical Genetics, University of Antwerp and Antwerp University Hospital, Antwerp, Belgium.
authors.forename: J K
authors.initials: JK
authors.lastname: Van Camp
authors.affiliation: Department of Medical Genetics, University of Antwerp and Antwerp University Hospital, Antwerp, Belgium.
authors.forename: V
authors.initials: V
authors.lastname: de Craemer
authors.affiliation: Department of Endocrinology, Diabetology and Metabolic Diseases, Antwerp University Hospital, Antwerp, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: Verrijken
authors.affiliation: Department of Paediatrics, Antwerp University Hospital, Antwerp, Belgium.
authors.forename: K
authors.initials: K
authors.lastname: Van Hoorenbeeck
authors.affiliation: Department of Paediatrics, Antwerp University Hospital, Antwerp, Belgium.
authors.forename: S L
authors.initials: SL
authors.lastname: Verhulst
authors.affiliation: Department of Paediatrics, Antwerp University Hospital, Antwerp, Belgium.
authors.forename: R P
authors.initials: RP
authors.lastname: Rooman
authors.affiliation: Department of Paediatrics, Antwerp University Hospital, Antwerp, Belgium.
authors.forename: K N
authors.initials: KN
authors.lastname: Desager
authors.affiliation: Department of Paediatrics, Jessa Hospital, Hasselt, Belgium.
authors.forename: G
authors.initials: G
authors.lastname: Massa
authors.affiliation: Department of Endocrinology, Diabetology and Metabolic Diseases, Antwerp University Hospital, Antwerp, Belgium.
authors.forename: L F
authors.initials: LF
authors.lastname: Van Gaal
authors.affiliation: Department of Medical Genetics, University of Antwerp and Antwerp University Hospital, Antwerp, Belgium.
authors.forename: W
authors.initials: W
authors.lastname: Van Hul
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics; D002648:Child; D004252:DNA Mutational Analysis; D017930:Genes, Reporter; D056726:Genetic Association Studies; D020022:Genetic Predisposition to Disease; D006801:Humans; D051379:Mice; D020125:Mutation, Missense; D009767:Obesity, Morbid / Q000235:genetics*; D010641:Phenotype; D012097:Repressor Proteins / Q000235:genetics; D015533:Transcriptional Activation
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D012097:Repressor Proteins; C491094:SIM1 protein, human; C101750:Sim1 protein, mouse